Chapter 8 



Individuality Differentials in Closely 

 Inbred Guinea Pigs 



Three series of experiments were carried out with guinea pigs. In the 

 first series (1927), the guinea pigs were closely inbred in the Depart- 

 ment of Agriculture in Washington, by Sewall Wright and O. N. 

 Eaton. In a second supplementary series (1931), these experiments were con- 

 tinued with guinea pigs inbred for a few additional generations, likewise in 

 the Department of Agriculture, by Hugh C. McPhee and O. N. Eaton ; and a 

 third, shorter and more recent series was carried out with guinea pigs closely 

 inbred for only five or six generations at the Caworth Farms. The guinea 

 pigs in the first series had been inbred by consecutive brother-sister matings 

 mostly for from 17 to 23 generations, while the large majority of those in the 

 second series had been inbred for from 20 to 25 generations. In the first series, 

 five inbred families were used, designated as 2, 13, 32, 35 and 39; 2N was a 

 line of family 2, selected for colored nose spots. This line was exceptional, 

 insofar as it was not strictly propagated by brother-sister matings, but mating 

 took place with a view of increasing the proportion of animals carrying this 

 characteristic nose spot, without regard to relationship. It happened, however, 

 that there were several brother-sister matings in this line, and in some in- 

 stances they were repeated for three or four successive generations, according 

 to information given me by Dr. O. N. Eaton. The degree of homogeneity in 

 the various families differed (Sewall Wright, Bull., U. S. Dept. Agriculture, 

 No. 1090). As controls, guinea pigs from a non-inbred B group and non- 

 inbred guinea pigs obtained from various dealers were used. In the second 

 series, only hybrids CY between families 2 and 13y, the latter an otocephalic 

 line of family 13, and hybrids CP between families 13y and 35 were used as 

 donors and hosts in the transplantation experiments. The figure following the 

 designation of the family indicates the number of consecutive brother-sister 

 matings. In the hybrids, the upper family represents the male and the lower 

 the female partner. The figure following CP or CY signifies the number of 

 generations of brother-sister inbreeding which the hybrids had undergone. 

 CP-0 and CY-0 represent the F lt CP-1 and CY-1 represent the F 2 generations, 

 and so on. The guinea pigs in these experiments ranged in weight between 200 

 and 500 grams. The examinations usually took place between the 20th and 60th 

 day, but in some experiments they were made as late as about Zy 2 and S l / 2 

 months following transplantation. We shall state the principal results obtained, 

 without distinguishing between series I and II. 



A. (1) Transplantations in the same inbred family, host and donor not 

 being nearly related. In transplantations from 32-17 to 32-19 and in other 

 similar transplantations in family 32 the grade was 3 + . This indicates auto- 



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